Recently, a so-called twin panel formed of two display panels has been heavily used in a portable device etc., particularly in a foldable mobile phone. FIG. 11 is a circuit diagram showing a twin panel 581 as an example of such a twin panel. The twin panel 581 is formed of a main panel 582 and a sub panel 583.
The main panel 582 includes a TFT substrate 584, which has a substrate and a thin film transistor (TFT) 592 provided thereon; a counter substrate 585, which faces the TFT substrate 584; and a liquid crystal layer (LC) 594, which serves as a display medium sandwiched between the TFT substrate 584 and the counter substrate 585.
Provided on the TFT substrate 584 are a plurality of gate bus lines 588 and a plurality of source bus lines 589. Disposed near a crossing of each gate bus line 588 and each source bus line 589 is a TFT 592. A gate of the TFT 592 is connected to the gate bus line 588. A source of the TFT 592 is connected to the source bus line 589. The drain of the TFT 592 is connected to a pixel electrode. Then, between the pixel electrode and the counter electrode (COM) 593 provided on the counter substrate 585, a voltage is applied to the LC 594 serving as a pixel. All of the TFTs 592 are respectively supplied with voltages, so that an image is displayed.
Further, the main panel 582 also has a gate driver 590 and a source driver 591. An outgoing line extending from the gate driver 590 is connected to the gate bus line 588, and an outgoing line extending from the source driver 591 is connected to the source bus line 589. Then, the gate driver 590 and the source driver 591 apply a gate signal voltage and a display data signal to the respective bus lines.
Meanwhile, the sub panel 583 includes a TFT substrate 586, which has a substrate and a thin film transistor 592 provided thereon; a counter substrate 587, which faces the TFT substrate 586; and liquid crystal layer (LC) 594, which serves as a display medium sandwiched between the TFT substrate 586 and the counter substrate 587.
The sub panel 583 is connected to the main panel 582 through a flexible printed circuit (FPC; not shown). This allows a gate signal voltage or a display data signal to be applied from the gate driver 590 and the source driver 591 of the main panel 582 through the wiring in the main panel 582 and the FPC to each bus line of the sub panel 583.
Provided on the TFT substrate 586 are a plurality of gate bus lines 588 and a plurality of source bus lines 589. Disposed near a crossing of each gate bus line 588 and each source bus line 589 is a TFT 592. A gate of the TFT 592 is connected to the gate bus line 588. A source of the TFT 592 is connected to the source bus line 589. A drain of the TFT 592 is connected to a pixel electrode. Then, between the pixel electrode and the counter electrode (COM) 593 provided on the counter substrate 587, a voltage is applied to the LC 594 serving as a pixel. All of the TFTs 592 are respectively supplied with voltages so that an image is displayed. This makes it possible to display an image on the main panel 582 or the sub panel 583.
Examples of such a device having a twin panel can be found in Tokukai 2001-067049 (Prior Art 1; published on Mar. 16, 2001), Tokukai 2001-282145 (Prior Art 2; published on Oct. 12, 2001), and Tokukai 2003-131250 (Prior Art 3; published on May 8, 2003).
Prior Art 1 discloses a foldable mobile communication terminal apparatus having a twin panel formed of a first liquid crystal display section (first liquid crystal display device) and a second liquid crystal display section (second liquid crystal display device). The mobile communication terminal apparatus has a body section, and a cover section (folder cover section) that is foldable/unfoldable relative to the body section. The first liquid crystal display section is provided on an inner surface of the cover section (inner surface in a folded state). The second liquid crystal display section is provided on an outer surface of the cover section (outer surface in a folded state). The first and the second liquid crystal display sections are driven by one driver, which is provided on the side of the first liquid crystal display section. That is, an output from the driver is input into the second liquid crystal display section through the first liquid crystal display section. The second liquid crystal display section has a smaller display area than the first liquid crystal display section (see FIGS. 4 and 5 in Patent Document 1). The second liquid crystal display section displays time and general information while the first liquid crystal display section displays various kinds of information. Only the second liquid crystal display section makes a display with the cover section closed, and only the first liquid crystal display section makes a display with the cover section opened.
As with Prior Art 1, Prior Art 2 discloses a foldable mobile phone with a twin panel formed of a first liquid crystal display section (inner liquid crystal display section) and a second liquid crystal display section (outer liquid crystal display section). The mobile phone has a body section (lower housing) and a cover section (upper housing) foldable/unfoldable relative to the body section. The first liquid crystal display section is provided on an inner surface of the cover section (inner surface in a folded state). The second liquid crystal display section is provided on an outer surface of the cover section (outer surface in a folded state). The first and the second liquid crystal display sections are driven by one driver, which is provided on the side of the first liquid crystal display section. That is, an output from the driver is input into the second liquid crystal display section through the first liquid crystal display section. The second liquid crystal display section has a smaller display area than the first liquid crystal display section (see FIGS. 3 and 4 in Patent Document 2). Only the second liquid crystal display section makes a display with the cover section closed, and only the first liquid crystal display section makes a display with the cover section opened.
As with Prior Art 1, Prior Art 3 discloses a foldable mobile phone with a twin panel formed of a first liquid crystal display section (LCD) and a second liquid crystal display section (LCD). The mobile phone has a body section and a cover section (lid) foldable/unfoldable relative to the body section. The first liquid crystal display section is provided on an inner surface of the cover section (inner surface in a folded state). The second liquid crystal display section is provided on an outer surface of the cover section (outer surface in a folded state). The first and the second liquid crystal display sections are driven by one driver, which is provided on the side of the first liquid crystal display section. That is, an output from the driver is input into the second liquid crystal display section through the first liquid crystal display section. The second liquid crystal display section has a smaller display area than the first liquid crystal display section (see FIGS. 1 and 10 in Patent Document 3). The second liquid crystal display section displays basic information such as a received call and date; the first liquid crystal display section displays main information.
One of the major demands for the twin-panel display device, which, as described above, is heavily used in a portable device such as a mobile phone, is reduction in power consumption. However, measures for reducing power consumption attempted in the conventional devices have not yet achieved sufficient power reduction.